This invention pertains to fluid delivery systems and, more particularly, to high specific speed impeller pumps.
A high specific speed impeller pump such as, for example, an axial inducer, comsumes more power under low or shut-off flow conditions than at design flow conditions. This is attributable to a characteristic pressure rise as the flow decreases below the optimum design flow.
Frequently, in fuel control applications, the pressure rise is far greater than that necessary to properly charge the inlet of the centrifugal pump with which the inducer is associated and consequently the increased power consumption is in no manner beneficial but only occasions an undesirable heating of the fluid being pumped. Since pumped fuel is often used for cooling electronic units, a smaller temperature rise in the pumped fluid enhances the cooling capacity of the fuel. It will also be appreciated that, because of the fact that fuel delivered to the burner nozzles of a gas turbine engine must not exceed a maximum safe temperature, heat rejection to the fuel by the pumping elements should be minimized, particularly if the fuel is used for cooling prior to reaching the pumping elements.